Persons may become confined to a support surface such as a bed, wheel chair, or other device, for a large variety of reasons (e.g., as a result of injury or illness or as a consequence of the requirements of a job function during employment). Also, elderly persons may be confined to beds or other devices for extended periods of time.
Decubitus ulcers, which are also referred to as pressure ulcers, pressure sores, and/or bedsores, are a pervasive problem in the health care field, with high cost both in terms of individual human suffering and in the financial cost to society. Decubitus ulcers are localized cellular necroses that tend to develop when soft tissue is compressed between a bony prominence and a firm surface for prolonged periods of time. External pressure exerts its influence by occluding blood flow, leading to ischemic injury. Interruption of blood flow, and hence oxygen supply, can cause a sequence of intracellular events to occur, which proceeds to an irreversible stage if the blood flow is not restored. Ischemic injury can result in cell death and the accumulation of cell debris within the tissues.
Factors affecting the formation of decubitus ulcers include the intensity and duration of the pressure being applied. If a patient remains immobile and in the same position for periods of time that are less than about two hours, the ischemia may be reversible and generally no long term or irreversible damage is done to the soft tissues (e.g., skin, subcutaneous tissues, and muscle) over bony prominences. However, if the period of immobility exceeds a certain threshold (e.g., about two hours), decubitus ulcers begin to form.
To prevent the formation of decubitus ulcers, it is the policy of many hospitals and institutions to reposition patients about every two hours. However, this practice can be physically intensive and less than effective. In addition, there is a trend towards the care of patients in the home, rather than in a hospital, and in such circumstances nursing care may not be available for twenty four hours/day.
There are a variety of systems available that are intended to reduce the formation of decubitus ulcers. Various previous approaches include static devices (e.g., foam mattresses, air mattresses, water beds and sheepskins), which attempt to redistribute support away from bony prominences, and active devices (e.g., alternating air mattresses), which function by alternately shifting support pressure.
One example of an active device is discussed in U.S. Pat. No. 5,010,608 to Barnett et al., which describes a support system having a plurality of separate cells that are alternately and repeatedly inflated. The distance between centers of adjacent cells is less than the human two-point discrimination threshold. However, such previous approaches have various drawbacks. For instance, the configuration (e.g., spacing, shape, etc.) of the separate cells in previous approaches can lead to drawbacks such as susceptibility to leaking, patient discomfort, and/or manufacturing inefficiency, among other drawbacks.